The invention relates to a series of new multifunctional inhibitors especially for industrial scale inhibition application. In particular, the invention relates to the use of a synergistic blend of phosphonates to prevent the formation of scale in aqueous systems by sequestration (or chelation) of various metal ions or by the so-called threshold inhibition reaction.
The components of the blend are known agents for scale control. Although these agents have various chemical names, depending inter alia on the field of use, their usual names and abbreviations in this field are 1-hydroxyethylidene-1,1-diphosphonic acid (abbreviated herein as HEDP); and diethylenetriaminepenta(methylenephosphonic acid) (abbreviated herein as DETPMP).
Mixtures of HEDP and DETPMP have been used on a limited commercial basis in textile preparation formulas primarily for alkaline peroxide bleach bath stabilization (serving a metal chelation function).
Mixtures of DETPMP and ATMP (aminotri(methylenephosphonic acid)) are also known, e.g. from UK 1,563,521, for a relatively narrow set of applications, all pertaining to cleaning surfaces with a dilute solution of alkali metal hydroxide (i.e. NaOH and phosphonate).
A sequestration (or chelation) agent works by forming a soluble (aqueous) metal-ligand complex. Chelating ties up the ion and prevents it from reacting to form a less soluble species. The chelation reaction is a stoichiometric reaction.
A threshold agent acts to prevent crystal nucleation from supersaturated salt solutions (aqueous). Since crystallization is a dynamic, reversible reaction, when one direction of the reaction is stopped, the net result is that the crystal may redissolve, releasing the threshold reagent back into solution. This is a sub-stoichiometric reaction requiring relatively small amounts of agent, relative to stoichiometric reaction requirements, to maintain a supersaturated solution.
The concentrations noted are the concentration for scale inhibition. In some special circumstances, e.g. oil well "squeeze" treatment (see discussion in U.S. Pat. No. 5,755,972)--an "infiltrating" solution is used at a much higher concentration in order to infiltrate the underground petroleum bearing formations. Thereafter, the anti-scaling agent leaches out over time to maintain the required concentrations in the water being treated. Additional infiltration treatment of the formations are made as required, to maintain leaching rates sufficient to maintain effective concentrations of the composition in the water being treated, to prevent scale formation.
Concentrations are given either in ppm by weight or in mg/liter. For most purposes, they can be used interchangeably. However, in high brine (or salt) concentration situations where the weight of the solution is substantially greater than for water, mg/liter is preferably used.